A Versatile Strategy\ntoward Donor–Acceptor\nNanofibers with Tunable Length/Composition and Enhanced Photocatalytic\nActivity

Living crystallization-driven self-assembly (CDSA) has\nemerged\nas an efficient strategy to generate nanofibers of π-conjugated\npolymers (CPNFs) in a controlled fashion. However, reports of donor–acceptor\n(D–A) heterojunction CPNFs are extremely rare. The preparation\nof these materials remains a challenge due to the lack of rational\ndesign guidelines for the D–A π-conjugated units. Herein,\nwe report a versatile CDSA strategy based upon carefully designed\nD–A-<i>co</i>-oligomers in which electron-deficient\nbenzothiadiazole (BT) or dibenzo[<i>b</i>,<i>d</i>]thiophene 5,5-dioxide (FSO) units are attached to the two ends of\nan oligo(<i>p</i>-phenylene ethynylene) heptamer [BT-OPE<sub>7</sub>-BT, FSO-OPE<sub>7</sub>-FSO]. This arrangement with the electron-deficient\ngroups at the two ends of the oligomer enhances the stacking interaction\nof the A–D–A π-conjugated structure. In contrast,\nD–A–D structures with a single BT in the middle of a\nstring of OPE units disrupt the packing. We employed oligomers with\na terminal alkyne to synthesize diblock copolymers BT-OPE<sub>7</sub>-BT-<i>b</i>-P2VP and BT-OPE<sub>7</sub>-BT-<i>b</i>-PNIPAM (P2VP = poly(2-vinylpyridine), PNIPAM = poly(<i>N</i>-isopropylacrylamide)) and FSO-OPE<sub>7</sub>-FSO-<i>b</i>-P2VP and FSO-OPE<sub>7</sub>-FSO-<i>b</i>-PNIPAM. CDSA\nexperiments with these copolymers in ethanol were able to generate\nCPNFs of controlled length by both self-seeding and seeded growth\nas well as block comicelles with precisely tunable length and composition.\nFurthermore, the D–A CPNFs with a BT-OPE<sub>7</sub>-BT-based\ncore demonstrate photocatalytic activity for the photooxidation of\nsulfide to sulfoxide and benzylamine to <i>N</i>-benzylidenebenzylamine.\nGiven the scope of the oligomer compositions examined and the range\nof structures formed, we believe that the living CDSA strategy with\nD–A-based co-oligomers opens future opportunities for the creation\nof D–A CPNFs with programmable architectures as well as diverse\nfunctionalities and applications.